The present invention relates to a method and an apparatus for examining if a miniaturized electronic part is correctly mounted in a predetermined position on a printed circuit board or the like.
Miniaturized electronic parts or microparts so-called chip elements are widely used nowadays in place of electronic parts with lead wires. Such a chip element is frequently mounted on a printed circuit board together with electronic parts with lead wires. During assembly of a circuit, chip elements are temporarily adhered in predetermined positions on a printed circuit board with an adhesive, hardened in a drying furnace, and soldered. Temporary adhesion of the chip element onto the printed circuit board is performed on an automatic manufacturing line for mass-producing printed circuit boards.
However, when the chip elements are temporarily adhered on the printed circuit board, the chip elements may become misaligned from their correct positions or separated from the printed circuit board, or may be adhered at wrong positions on the printed circuit board. If such an error is found after soldering, much labor is required to correct it, resulting in higher manufacturing cost or a lower yield of the printed circuit boards. For this reason, it is very important to identify before soldering any adhesion of the chip elements at erroneous positions or separation of the chip elements, and to correct the same.
Misalignment or separation of chip elements after adhesion are conventionally identified by visual observation which requires much labor and is inefficient and unreliable.
It is also proposed to process image data of a printed circuit board having chip elements mounted thereon, where the data is obtained by an image pickup camera, so as to examine misalignment or separation of the chip elements. However, correct examination is still difficult by this method due to misalignment of the printed circuit board during examination, or warp or distortion of the printed circuit board. The surface of a printed circuit board on which the chip elements are mounted also has a printed wiring pattern of copper foil or printed characters formed thereon. For this reason, a highly complex pattern recognition technique of image data is required to identify the chip elements from such patterns. Such a highly complex pattern recognition technique is also subject to examination errors.